Temperature fields for Jupiter's upper troposphere were derived from thermal
radiometric observations of discrete regions by the Galileo
Photopolarimeter-Radiometer (PPR), on orbits Ganymede-1, Europa-6, and
Ganymede-7, often in concert with other Galileo remote sensing instruments.
A large set of synoptic earth-based observations of both reflected sunlight and
thermal emission enabled more global comparisons. The coldest region of the
planet was at the center of the Great Red Spot (GRS), whose bright southern
region detected in the June, 1996, Ganymede-1 orbit encounter (Orton
et al., 1996, Science274, 388) continued through the April,
1997, Ganymede-7 orbit encounter. These
spatially denser G7 GRS observations show that much of the warm ring
at the GRS exterior edge is surrounded by a narrow, cool band near the
2000-km resolution limit of the PPR, suggesting a region of upwelling,
expanding gas. Smaller anticyclonic
vortices, such as the classical white ovals in the southern hemisphere, are
also colder than their surroundings, and the nearby cyclonic regions are
warmer, suggesting a series of upwelling, divergent areas interspaced with
downwelling, convergent ones. The relatively warm North Equatorial Belt
(NEB) contains considerable thermal heterogeneity, often with variability
unrelated to the cloud field. On the other hand, 5- m hot spots,
among the clearest and driest regions of the planet and considered to be the
best examples of strong downdrafts, are not characterized by relatively
warm temperatures. While this might imply that the main convergence is deeper
in the troposphere, it might also imply much of the surrounding region near
this latitude is already downwelling under fully adiabatic conditions.